TT won't let me claim MN k-12 education subtraction. I don't believe there is any income limit and all it requires is a child in K-12 school and educational expenses.

Yes, there is no income limitation.  The subtraction is an adjustment to income for educational expenses paid for K-12 student qualifying children.  A qualifying child for this subtraction is the same definition as for Federal Earned income tax Credit. A qualifying child is:

1. Younger than the taxpayer and under age 19, or under age 24 and a full-time student, or any age and permanently and totally disabled,
2. Who lived with the taxpayer for more than half of the year, and
3. Who did not provide over half of his or her own support,
4. Who is the taxpayer’s son, daughter, stepchild, foster child, brother, sister, stepbrother, stepsister, half brother, half sister, or a descendent of any of them (for example, a grandchild, niece, or nephew).

Generally, any purchase related to K-12 educational expenses or after school programs qualify.  The adjustment is taken on Sch M1M as a subtraction from Minnesota income.  Here is a link with more specific information on this program